Unfortunately your site has been hacked. Follow the vBulletin recommendations, I have posted below. Be thorough when using the recommendations.
Double check your system by using the best practices listed below.
Then please read the following two blog posts:
http://www.vbulletin.com/forum/blogs...ve-been-hacked
http://www.vbulletin.com/forum/blogs...vbulletin-site
Also please see these recent security announcements:
http://www.vbulletin.com/forum/forum...-1-vbulletin-5
http://www.vbulletin.com/forum/forum...d-all-versions